Molecular Mechanism Of Nutritional And Developmental Regulation In Langshan Chicken

We investigated changes in mRNA expression of the somatotropic,thyrotropic,and corticotropic axes from slower growing Langshan(LS) layer and more rapidly growing Arbor Acres(AA) broiler chickens during embryonic and postnatal development.Real time RT-PCR was used to quantify the level of transcription in the hypothalamus,pituitary,liver, breast muscle and epiphyseal cartilage.Nutrient availability may control body growth directly and indirectly through its influence on regulatory factors.Moreover,AA chickens were fed a nutrient-rich AA diet(AA,as a control group) and LS chickens were fed either a less-nutritious LS diet(LL) or the AA diet(LA).For evaluating the effects of the diet on gene expression in general at the postnatal day 14(P14),P28 and P42 of LL,LA and AA groups chickens,the General Linear Models(GLM) procedure(with developmental age and strain as fixed factors) of SPSS software was used to analyze the effects of nutrient availability on the strain difference between LL,LA and AA.Our data show the first evidence that certain genes may be correlated during specific developmental periods and that strain differences in the expression of those genes in LS and AA chickens are due to differential responses to the same AA diet.These findings may help improve the molecular breeding of chickens.1.Expression of genes involved in the somatotropie,thyrotropic,and corticotropic axes during development of Langshan and Arbor Acres ChickensWe found an inverse expression profile between pituitary growth hormone(GH) and hepatic GH receptor(GHR) mRNA(postnatal day 28[P28]-42),insulin-like growth factor (IGF)-Ⅰand IGF-IR(P0-42),respectively.Hepatic IGF-Ⅰwas a major point of control in the GH/IGF axis during P0-P28.Pituitary GH-releasing hormone(GHRH) receptor(GHRHR) may serve an autocrine/paracrine function during P0-28,and hypothalamic ghrelin may affect growth by stimulating the release of hepatic IGF-Ⅰduring embryonic day 8(E8)-P28. Hypothalamic ghrelin might interact with ccorticotrophin-releasing hormone(CRH) during P0-P28.Hepatic IGF binding protein(IGFBP)-2 regulated growth by regulating hepatic IGF-Ⅱbioavailability during P0-P42.Hepatic IGFBP-5 was an important IGF mediator.A co-expression profile was found between hypothalamic GHRH(E10-E16 and P0-P42), somatostatin(SS;P0-P28),thyrotropin-releasing hormone(TRH;E10-E16 and P0-P28), ghrelin(P0-P42),and pituitary GH mRNA,hypothalamic SS(P0-P28),CRH(P0-P42), TRH(E10-E18 and P0-P42),and TSHβmRNA,respectively.GLM analysis revealed that LL chickens expressed significantly higher levels of pituitary GH,hypothalamic SS, Ghrelin,and hepatic IGF-IR mRNA than AA chicken while the opposite was true for BW, hepatic IGF-Ⅰand GHR mRNA,although strain differences on some age group were not statistically significant When comparing LS and AA chickens under the same AA diet containing higher nutrient compositions,strain differences in pituitary GH,hypothalamic SS,Ghrelin,hepatic IGF-Ⅰand GHR mRNA disappeared,while strain differences in body weight(BW) and hepatic IGF-IR mRNA still existed,which provide the new nutrient data for the application of chickens molecular breeding.Our data indicates the selected genes may be parallel expression in certain periods and strain differences in genes expression respond to nutrition differently in the hypothalamus,pituitary and liver from LS and AA chickens.2.Investigation of the insulin-like growth factor system in breast muscle during development in Langshan and Arbor Acres chickensWe analyzed the effects of nutrient availability on the breast muscle insulin-like growth factor system.According to our results,IGF-Ⅱ(E16-P42),IGF-IR(E18-P42),and IGFBP-2 (E18-P42),-5(E16-P14),-7(E12-P0),and-3(E12-P0) were positively correlated with IGF-Ⅰ,while IGFBP-3(P0-P28) was negatively correlated with IGF-Ⅰ.In comparison, IGF-IR(E18-P42),IGFBP-2(E18-P42),-5(E14-P0),and -3(E16-P0) were positively correlated with IGF-Ⅱ,while IGF-IR(E10-E16) and IGFBP-3(P0-P28) were negatively correlated with IGF-Ⅱ.Moreover,IGFBP-2(E16-P42),-7(E10-E16),and -3(E10-E16) were positively correlated with IGF-IR,while IGFBP-3(P0-P28) was negatively correlated with IGF-IR.Finally,IGFBP-7(E12-P0) was positively correlated with IGFBP-3,while IGFBP-2(P0-P28) and -7(P0-P42) were negatively correlated with IGFBP-3.Overall,the AA chickens exhibited higher levels of IGF-Ⅰ,IGF-IR,and IGFBP-2 mRNA expression than the LL chickens,while the opposite was true for IGFBP-7.No strain differences in IGF-Ⅰ,IGF-IR,and IGFBP-7 mRNA expression were detected any more between LA and AA chickens;however,a strain difference was still observed for IGFBP-2.LA chickens exhibited higher levels of IGFBP-2 than LL chickens,while the opposite was true for IGFBP-7.Our data show the first evidence that certain IGF system genes may be correlated during specific developmental periods and that strain differences in the expression of those genes in LS and AA chickens are due to differential responses to the same diet in the breast muscle.3.Role of the insulin-like growth factor system in epiphyseal cartilage on the development of Langshan and Arbor Acres chickens Gallus domesticusWe measured the mRNA transcript expression patterns for members of the insulin-like growth factor(IGF) system during embryonic and postnatal development in epiphyseal cartilage from LS and AA chickens Gallus domesticus.IGFBP-2 expression was positively correlated with expression of IGF-Ⅰfrom E14 to P0 and with IGF-Ⅱfrom E14-F14 but negatively correlated with IGF-Ⅰfrom P0-P42 and IGF-Ⅱfrom P14-P42.Expression of IGFBP-5 correlated positively with the expression of IGF-Ⅰfrom E14-P0 but negatively from P0-P28.The results suggest that these IGF axis genes are regulated in a coordinated fashion during development.An inverse expression profile was found between IGFBP-7 and IGF-Ⅱduring P0-P42.A co-expression profile was found between IGFBP-3(E14-E18, P14-P42) and IGF-IR,and between IGFBP-3(E14-P0,P 14-P42) and IGF-Ⅰ.The endocrine factors can be integrated with nutrition to regulate animal growth.In our study,AA chickens were fed a nutrient-rich AA diet,and LS chickens were fed either an AA diet(LA) or a less-rich diet(LL).GLM analysis revealed that IGF-Ⅰ,IGFBP-2,and IGFBP-3 mRNA expression was higher in AA chickens than in LL chickens,while the opposite was true for IGF-Ⅱand IGFBP-7,although the strain differences in some age groups were not significant.LS and AA chickens fed the same AA diet showed no differences any more in IGF-Ⅰ,IGFBP-2,IGFBP-7,and IGFBP-3 transcription,but did still show differences in IGF-ⅡmRNA expression.These findings may help to improve the molecular breeding of chickens.